The effectiveness and performance of printed circuit boards are continually being upgraded by the use of more complex solid state circuit technology, the use of higher frequency operating signals to improve circuit response times and by increasing the circuit density of the boards. The upgrade in printed circuit board technology, in turn, has placed more stringent requirements upon the design of electrical connectors. The need exists for electrical connectors having increased input/output densities and decreased contact interconnect spacing, improved electrical performance, high mechanical integrity, improved reliability and greater flexibility. Additionally, the electrical connectors should be adapted for surface mount technology and for effecting printed circuit board mating with low insertion forces.
Prior art electrical connectors for electrically interconnecting printed circuit boards have traditionally been fabricated using stamped and formed contacts and molded dielectrical material. These prior art electrical connectors have been limited to contact interconnect spacing on the order of 40 contact interconnects per linear inch. In addition, prior art contact interconnect matrices have been formed as distributed pluralities of signal, ground and power contact interconnects, typically in a ratio of 6:3:1, respectively.
For example, if a particular application requires 300 signal contact interconnects, the contact interconnect matrix must be formed to have 500 contact interconnects since 150 ground contact interconnects and 50 power contact interconnects are required. With a contact interconnect density of 40 contact interconnects/linear inch, a single row of 500 distributed signal, ground and power contact interconnects would occupy 12.50 linear inches of board space, thus limiting the input/output density of the electrical connector.
To satisfy the input/output densities required by present day circuit board technology, contact interconnect spacing on the order of 80 contact interconnects/linear inch is required. While electrical connectors are available which have contact interconnect spacing on the order of 80 contact interconnects per linear inch, these electrical connectors utilize interconnect matrices having distributed signal, ground and power contact interconnects. Thus, even electrical connectors having contact interconnect spacing on the order of 80 contact interconnects per linear inch provide only a limited increase in input/output density. For example, a single row of 500 distributed signal, ground and power contact interconnects would occupy 6.25 linear inches of board space.
Higher frequency signals are increasingly being utilized with printed circuit boards to improve the response time of the circuits. The use of higher frequency signals, however, presents additional design constraints upon designers of electrical connectors. The frequency response curve for low to middle frequency signals is illustrated in FIG. 1A wherein t.sub.r represents the rise time of the signal, t.sub.s represents the settling time of the signal, t.sub.ss represents the steady state or operational condition of the signal, and t.sub.f represents the fall time of the signal. To increase circuit performance, t.sub.r and t.sub.s should be minimized to the extent practicable.
One means of improving circuit performance is by reducing the t.sub.r of the signal. Higher frequency signals improve the response time of a circuit by significantly reducing t.sub.r. A typical signal response curve for a high frequency signal is illustrated in FIG. 1B. The high frequency signal has a t.sub.r approximately one order of magnitude lower than a low frequency signal, i.e., 5 nanoseconds versus 0.30 nanoseconds. As will be apparent from an examination of FIG. 1B, however, higher frequency signals may have a relatively longer t.sub.s due to impedance mismatches and/or discontinuities in the signal conducting paths. Therefore, a prime concern in designing electrical connectors is to ensure matched impedances between the electrical connector and the contact interconnects of the mated printed circuit boards and signal path integrity in the electrical connector.
A further problem area for electrical connector is the effect of contamination and/or oxidation on contact interconnects. Concomitant with an increase in input/output density of contact interconnects is the decrease in size of the contact interconnects. The reduction in size of the contact interconnects aggravates the detrimental effects of contamination and/or oxidation of the contact interconnects such as increased contacting resistances and distortion of electrical signals. Therefore, an effective electrical connector should have the capability of providing a wiping action between the contact interconnects of the printed circuit boards and the electrical connector.
The use of flexile film having preformed contact interconnects and interconnecting circuit traces is known in the art. Electrical connectors must be capable of effecting repetitive connections/disconnections between printed circuit boards. Repetitive connections/disconnections cause repetitive wiping action of the contact interconnects which may cause an undesirable degradation in the mechanical and electrical characteristics of the contact interconnects and/or the integrity of the signal paths of the electrical connector and/or printed circuit boards.
Finally, electrical connectors require some mechanical means for camming to provide the capability for printed circuit board mating with low insertion mating forces and to effect the wiping action between the contact interconnects. Ideally, the camming means should be a simple mechanical configuration and easily operated, thereby reducing the costs and time attributed to the manufacture and/or assemblage electrical connector. Representative camming mechanisms are shown in U.S. Pat. Nos. 4,629,270, 4,606,594 and 4,517,625. An examination of these patents reveals that the camming mechanisms disclosed therein are relatively complex mechanical devices requiring the fabrication and assemblage of a multitude of components. While these camming mechanisms may be functionally effective to provide a wiping action between contact interconnects, such camming mechanisms are relatively bothersome to fabricate and assemble. In addition, complex camming mechanisms significantly reduce the reliability and flexibility of the electrical connector.